Be honest. Don't make feeble attempts to end the relationship by being distant or elusive. Don't make excuses or beat around the bush. Set some time apart when you and your soon-to-be ex-significant other can be alone to talk. Approach the subject calmly and honestly. Tell him in the most delicate yet honest way that you can that you want to end the relationship. No matter how you go about breaking the news, the other person is going to be hurt, but the manner in which you do so can help lessen the blow.
Provide an explanation as to why you want to end the relationship. Don't just say, "I don't love you anymore," or "I don't feel the same." Be specific and use concrete examples. Point out ways in which you are not compatible. Mention the fact that you have both tried to make the relationship work and have put your all into it only to find the same patterns repeating themselves again and again. The fact that the relationship continues to fall short of what you both want is another sign of incompatibility.
Attempt to help your significant other see the end of the relationship as the beginning of a new opportunity to move forward with his life, meet new people and seize new opportunities. Use positive speech and mannerisms when talking.
Express your desire to remain friends. Point out that relationships don't have to end on bad terms and some ex-partners do remain friends for life.
Accept the fact that your ex-significant other is probably going to be hurt and angry at you for breaking up with him. It is normal to feel that way under the circumstances. Acknowledge hisfeelings but don't get into a verbal or physical altercation. You've said what you needed to say, so walk away and let go. Give him time. Your ex-significant other will come to terms with the end of the relationship in his own time. It takes time to heal and recover from the break up of a relationship.